[pure-silver] Agfa Sistan
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 27 May 2005 17:00:04 -0700
----- Original Message -----
From: "Graham Hughes" <graham@xxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, May 27, 2005 4:30 PM
Subject: [pure-silver] Re: AgfaPhoto Insolvency
> On May 27, 2005, at 14:50, Richard Knoppow wrote:
>> I know whats in Sistan but not its actual formula.
>> Fuji
>> makes a stabilizer called Ag Guard. Its evidently not the
>> same substance as Sistan but serves the same purpose.
>> Both
>> are stabilizers for the image silver where toning is not
>> desirable. Fuji did publish some limited research on
>> Ag-Guard. It shows that its effective in preventing
>> oxidation and sulfiding of the image but is not as
>> effective
>> as toning.
> I've heard of that, but it's unobtainable in the US as far
> as I can
> tell. The main reason I like Sistan over toning is I can
> use it on
> film; also that it doesn't require quite the same care
> that the
> toners I'm familiar with do. If I can't get access to
> Sistan I
> probably won't be able to get access to Viradon either,
> but KBT is
> potentially practical; however, it will only be practical
> for paper
> as far as I know. I know there was a lot of microfilm
> research that
> examined toning film in selenium toners, but I don't think
> they cared
> as much about the change in color as I would (since if the
> emulsion
> changes color it will change the effect of VC filters;
> selenium's
> intensifying properties would also be undesirable in a
> negative).
> Thus my concern.
>
> If there's anywhere that imports Ag Guard into the US,
> then I'd like
> to hear about it as a contingency.
>
> Graham
I am not quite sure what IPI's position on the preferred
method of protecting microfilm is at present. However, they
developed a low odor polysulfide toner as a standard
treatment several years ago. KBT works as well but the IPI
toner is made up by the user so it is not subject to
unexpected changes. KBT will protect microfilm without
changing the image structure excessivly so it should be
suitable for pictorial films as well. One of the advantages
of polysulfide toners is that they do not split-tone. That
is, they tone all densities equally. The problem with Kodak
Selenium toner was that, in the low concentration used for
microfilm, it did not tone low densities enough leaving them
subject to oxidation. Actually, KRST will protect film or
paper fully if toning is carried out far enough. Far enough
will cause some change in image color and/or density in most
materials. Dr. Nishimura stated to me that 3 minutes in a
1:9 solution of KRST will provide adequate protection.
IPI published criteria for toning microfilm with their
polysulfide toner but I don't know if they are applicable to
pictorial materials.
Gold toner also remains a standard for microfilm but its
expensive and also can cause some change in color or
density.
AFAIK, no real accelerated aging research has ever been
carried out on Sistan. It undoubtedly works but there is no
data to compare to toners.
FWIW, the most stable images are those _completely_ toned
in a sulfiding toner or Selenium toner.
Sistan has the virtue of not changing the appearance of
display prints while offering a substantial amount of
protection for them. Displayed prints are, of course,
particularly vulnerable because of their constant exposure
to atmospheric polutants.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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